No abstract

The current research aims to reconstruct sources of the rocks and pyroclastic input in the epeiric sea of the Eastern Russian Platform in the Latest Jurassic. Nine samples of the Volgian mudrocks, black shales, and sandstones from the Tatar Shatrashany borehole section and Gorodischi outcrop were investigated using the mineralogical, ICP-MS, XRD, electron microscopy, and Raman spectroscopy analyses. Accessory minerals of various mineral associations identified in sandstones indicate the input of terrigenous material from different sources. The Paleozoic deposits of the Volga-Ural and Voronezh Uplifts, igneous and metamorphic rocks of the Voronezh Crystalline Massive (including Pavlovsk granite complex), Ural Folding Region, and Baltic Shield were found to be the most likely sources. The morphology of zircons revealed their association with felsic alkaline rocks. Volcanic glasses and "camouflaged" pyroclastic material (heulandite, smectite, and mixed-layer mineral) were identified in mudrocks and black shales. The proportion of both smectite and mixed-layer mineral varies from 20% to 27% throughout the section, whereas the amount of heulandite reaches 25% in the Promzino black shales. The Raman spectroscopy analysis showed the intermediate-acid composition of volcanic glasses from the Promzino Formation. According to the results obtained in the study, volcanic arcs of the north margin of the Tethys and the High Arctic Large Igneous Province are the major sources of the pyroclastic material.

Human intervention in the geological environment is commonly thought to pose a threat to geoheritage. However, new information from the Western Caucasus where unique geological features are concentrated in Mountainous Adygeya, implies that man-made features in fact add value to geoheritage. Such features include a lengthy artificial niche in the Guama Gorge, accumulations of large artificial clasts along the road leading to the Lagonaki Highland and the Khadzhokh Quarry with the artificial Red Lake. These contribute to the regional uniqueness of geosites and can be classified as geomorphological, sedimentary, economical and hydro(geo)logical geoheritage types. Interestingly, these artificial features have natural analogues in the study area. Such integrity of local geological landscapes urgently require special interpretations for guided excursions and explanatory panels for correct comprehension of the origin of these unique features on the part of unprepared tourists. Generally, the human imprint on geological landscapes of Mountainous Adygeya is significant and occasionally positive, which makes the entire geodiversity hotspot of special, international interest and an object for further investigations.

. Widespread “camouflaged” pyroclastics including smectite, illite-smectite and heulandite are detected in the upper jurassic– lower cretaceous deposits of the Ulyanovsk-Saratov basin. Moreover, volcanic glasses are found in several stratigraphic units. The quantity of pyroclastic material in the study section (17–72%) is probably related to volcanic input in the basin. Concentrations of the trace and rare earth elements point to a predominantly acid source of ash material, except the Promzino and Ulyanovsk black shale formations linked to the mixed andesite-basaltic and felsic sources. Island arcs of the Northern Tethys basin and the High-Altitude Arctic Igneous Province are regarded as probable sources of the pyroclastic influx in the epeiric basin of the Russian Platform in the Jurassic-Early Cretaceous.

Quartz grains were separated by standard sieving of the Paleogene sands from the Sosnovka Formation of the Ulyanovsk-Syzran Volga region, which are a scarce and valuable raw material for glass making and construction. In order to establish the origin of the sands and restore the facies conditions of their formation, the surface microtextures of the separated quartz grains were examined by optical and electron microscopy. It was shown that the clastic grains of the Sosnovka sands bear the signs of a multi-stage formation process under the conditions of subaquatic (beach zone), eolian, mixed subaquatic-eolian (coastal dunes), injective, and continental pedological settings. For the first time, a complex of microtextures characteristic of the extrusion of grains from deep horizons under pressure and inherent in the injection mechanism of sand formation was described. The diagnostic complex of injectites includes rotational microtextures, notched microtroughs, and deformed fluid inclusions. The rather fresh appearance of the listed microtextures suggests that they were superimposed on the coastal-marine and eolian stages of the evolution with the subsequent formation of sand intrusions. At the final stage of the geological history of the Sosnovka sands, the grains were shaped by the continental pedological conditions, when secondary silica in the form of globules and their clusters cemented the quartz grains, the surface of which concatenated the features of the previous stages. Based on the results of the study, an interpretation scheme summarizing various microtextural features of the reconstructed paleoenvironments and the stages of formation the Sosnovka sands was developed. The finding that the Sosnovka sands are sand intrusions is of great practical importance, as it necessitates new approaches to the discovery and prediction of glass and quartz sand deposits confined to the Paleogene Sosnovka Formation of the Ulyanovsk-Syzran Volga region.